The present invention relates generally to a fibre optical system for pressure measurement. However, although the invention is directed to fibre optical systems with ability to carry out pressure measurements such systems may be configured to be used to measure other physical quantities, such as temperature. Furthermore, fibre optical systems for measuring static and/or dynamic pressures are comprised.
Fibre optical systems have several advantages over systems based on electronic sensors, since transmission of signals through optical fibres is not sensitive to electromagnetic noise, so that a preferred use of such fibre optical systems for pressure measurements is where severe electromagnetic disturbances may occur. Furthermore, optical pressure sensor elements of such systems can have a higher temperature capability than corresponding electronic sensors.
The present invention relates more particularly to a fibre optical system for pressure measurement comprising                a pressure sensor element having at least two parallel partially reflecting surfaces, one of which is arranged on a diaphragm movable with respect to another fixed said surface as a consequence of pressure differences across said diaphragm, said surfaces are arranged so as to cause interference phenomena of light inciding substantially perpendicularly onto and reflected by the two surfaces depending upon the actual distance between these surfaces,        a light source configured to emit light,        an optical fibre configured to receive and transmit light from said light source to said pressure sensor element in one direction and a measurement signal in the form of light reflected by said surfaces in the opposite direction, and        an arrangement configured to receive said measurement signal and evaluate this signal so as to determine a value of a pressure at said diaphragm,as well as use of such a system.        
A fibre optical system of this type is known through for example SE 510 449 and US 2002/0003917 A1 and is accordingly based on studying interference phenomena of light inciding upon said two surfaces of a so-called Fabry-Perot cavity for determining a pressure value. These interference phenomena will then be a function of the distance separating said two surfaces and accordingly the movement of said surface on the diaphragm with respect to the other, fixed surface. Such known fibre optical systems are able to deliver reliable pressure measurements in many situations, but it is an on-going attempt to improve such systems for making the measurements more reliable and extend the field of use of such fibre optical systems.